Device and method for belt speed control, and image forming apparatus

1. A device for controlling speed of a belt, wherein a scale including a plurality of equally spaced marks is attached to the belt in a direction of movement of the belt such that a gap is formed between a first end and a second end of the scale, the device comprising:

a first sensor configured to detect the marks on the scale and output a first signal upon detecting a mark among the marks;

a second sensor configured to detect the marks on the scale and output a second signal upon detecting a mark among the marks, wherein the first sensor and the second sensor are located at different positions along the direction;

said first and second sensors being configured to detect said gap; and

a controlling unit that controls the speed based on any one of the first signals and the second signals according to a position of the gap detected by the first sensor and the second sensor, wherein

the controlling unit switches from controlling the speed based on the first signals to controlling the speed based on the second signals at a timing immediately before the first end reaches the first sensor, wherein the timing is calculated when the second sensor detects the first end based on the distance corresponding to the space between the first sensor and the second sensor.

2. The device according to claim 1 , wherein

the second end is positioned upstream than the first end in the direction,

the second sensor is positioned upstream than the first sensor in the direction, and

the controlling unit switches from controlling the speed based on the first signals to controlling the speed based on the second signals after the second sensor detects the second end and before the first sensor detects the first end.

3. The device according to claim 1 , wherein

the controlling unit switches from controlling the speed based on the first signals to controlling the speed based on the second signals after the first end moves a distance corresponding to the gap from when the second sensor detects the first end and before the first end moves a distance corresponding to a space between the first sensor and the second sensor from when the second sensor detects the first end.

4. The device according to claim 1 , wherein

the controlling unit controls the belt such that the gap is not positioned between the first sensor and the second sensor while a driving source that drives the belt is starting up.

5. A device for controlling speed of a belt, wherein a scale including a plurality of equally spaced marks is attached to the belt in a direction of movement of the belt such that a gap is formed between a first end and a second end of the scale, the device comprising:

a first sensor configured to detect the marks on the scale and output a first signal upon detecting a mark among the marks;

a second sensor configured to detect the marks on the scale and output a second signal upon detecting a mark among the marks, wherein the first sensor and the second sensor are located at different positions along the direction;

said first and second sensors being configured to detect said gap; and

a controlling unit that controls the speed based on any one of the first signals and the second signals according to a position of the gap detected by the first sensor and the second sensor, wherein

the second end is positioned upstream than the first end in the direction,

the second sensor is positioned upstream than the first sensor in the direction, and

the controlling unit switches from controlling the speed based on the second signals to controlling the speed based on the first signals after the first end moves a distance corresponding a space between the first sensor and the second sensor in addition to a distance corresponding to the gap from when the second sensor detects the first end.

6. An image forming apparatus comprising:

an image forming unit that forms images by movement of a belt, wherein a scale including a plurality of equally spaced marks is attached to the belt in a direction of movement of the belt such that a gap is formed between a first end and a second end of the scale; and

a device that controls speed of the belt, including

a first sensor configured to detect the marks on the scale and output a first signal upon detecting a mark among the marks;

a second sensor configured to detect the marks on the scale and output a second signal upon detecting a mark among the marks, wherein the first sensor and the second sensor are located at different positions along the direction;

said first and second sensors being configured to detect said gap; and

a controlling unit that controls the speed based on any one of the first signals and the second signals according to a position of the gap detected by the first sensor and the second sensor, wherein

the controlling unit switches from controlling the speed based on the first signals to controlling the speed based on the second signals at a timing immediately before the first end reaches the first sensor, wherein the timing is calculated when the second sensor detects the first end based on the distance corresponding to the space between the first sensor and the second sensor.

7. The image forming apparatus according to claim 6 , wherein

the second end is positioned upstream than the first end in the direction,

the second sensor is positioned upstream than the first sensor in the direction, and

the controlling unit switches from controlling the speed based on the first signals to controlling the speed based on the second signals after the second sensor detects the second end and before the first sensor detects the first end.

8. The image forming apparatus according to claim 6 , wherein

the controlling unit switches from controlling the speed based on the first signals to controlling the speed based on the second signals after the first end moves a distance corresponding to the gap from when the second sensor detects the first end and before the first end moves a distance corresponding to a space between the first sensor and the second sensor from when the second sensor detects the first end.

9. The image forming apparatus according to claim 6 , wherein

the second end is positioned upstream than the first end in the direction,

the second sensor is positioned upstream than the first sensor in the direction, and

the controlling unit switches from controlling the speed based on the second signals to controlling the speed based on the first signals after the first end moves a distance corresponding a space between the first sensor and the second sensor in addition to a distance corresponding to the gap from when the second sensor detects the first end.

10. The image forming apparatus according to claim 6 , wherein

the controlling unit controls the belt such that the gap is not positioned between the first sensor and the second sensor while a driving source that drives the belt is starting up.